Inspired by a drawing posted on airradsirens.com some time ago, a huge siren that is a hybrid of a Thunderbolt and a Hurricane siren, supercharged by a large industrial air compressor. You DO NOT want to be anywhere close to this beast when it goes off!

@ ZiM972, not an actual siren, but it was done taking a recording of a single toned T-bolt siren, double tracking it, lowering the pitches of each track and pitch shifting one of them, then putting the air compressor at the beginning.